With the rapid development of world economy, the degree of dependence of people on fossil resources is gradually increased. The high-strength mining and consumption of the fossil resources cause emission of a great amount of harmful gases such as CO2 (Progress in Chemistry, 2006, 18(2-3): 131-141), which consequently leads to serious environmental pollution and influences the existence and development of the human society. In recent years, in order to relieve the increasing shortage of energy and the crisis of global environmental temperature rise caused by the increase of greenhouse gas emission, people are successively devoted in developing “green” alternative energy. As new renewable energy, fuel ethanol has the features of cleanness, renewability and the like, can reduce the emission of carbon monoxide and hydrocarbon in automobile exhaust, and is one of major countermeasures for effectively relieving the energy crisis.
The production of bioethanol is mainly to convert various biomasses into fuel ethanol through microbial fermentation. Reducing the production cost is a key factor for improving the economic benefit of production of fuel ethanol, especially cellulosic ethanol, and enabling it to be widely applied. In order to effectively reduce the production cost, currently people are mainly devoted in improving the fermentation time, improving the cyclic utilization efficiency of yeast and improving the endpoint ethanol concentration. Kwang Ho Lee, et al. ((Bioresource Technology, 102, 2011: 8191-8198) reported a method for immobilizing yeast by using calcium alginate as a carrier. Compared with free cells, immobilized yeast can obtain higher ethanol yield and can effectively shorten the fermentation time by 10 h; U.S. patent US20110201093A1 reports that the ethanol yield can be improved and the fermentation time can be reduced by adding carbonate into the fermentation medium; and the patents US20100143993A1 and WO2010/065595A2 adopt ionic liquid as an extraction agent to continuously extract ethanol in situ from the fermentation system to guarantee the activity of yeast.
Very high gravity (VHG) fermentation is a technique capable of improving the economic indicator of ethanol fermentation. The VHG ethanol fermentation has the following advantages: 1) the productivity and utilization rate of unit equipment are improved; 2) water consumption is reduced; 3) the ethanol in mash in unit volume is increased, and the energy consumption in cooking, fermentation, distillation and DDGS concentration and drying processes is reduced; and 4) the growth of contaminating microorganisms is inhibited. However, VHG ethanol fermentation also causes some problems for a reason that the starting sugar concentration is obviously increased. On one hand, since the yeast cells are stressed by high osmotic pressure under the effect of high sugar concentration, consequently the growth and survival rate are decreased, the fermentation time is prolonged and the fermentation is incomplete; on the other hand, the yeast cells are inhibited by strong products of high-concentration ethanol; the fermentation is also inhibited by nutrient insufficiency. The literatures (Biomass and Bioenergy 39, 2012:48-52) and (Energies 2012, 5, 3178-3197) discussed about improving the endpoint ethanol concentration by adding different types of nitrogen sources under VHG ethanol fermentation conditions.
The present invention discloses a surfactant-improved ethanol fermentation method, wherein high-activity saccharomyces cerevisiae is adopted, glucose is used as a raw material, a nonionic surfactant is added during fermentation cultivation to reduce ethanol inhibition, thereby the osmotic pressure caused by high sugar concentration is reduced, the survival rate and growth speed of the saccharomyces cerevisiae cells under special environments are improved, finally the endpoint ethanol concentration is improved and the consumption of water in the fermentation process and the consumption of energy in the distillation process are effectively reduced; and in addition, the yeast and the surfactant are separated from the fermentation mixture and then are reutilized in the next batch of fermentation processes.